Inkjet printing is a non-impact method for producing printed images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital data signals. There are various methods that can be utilized to control the deposition of ink droplets on the image-recording element to yield the desired printed image. In one process, known as drop-on-demand inkjet, individual ink droplets are projected as needed onto the image-recording element to form the desired printed image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. In another process, known as continuous inkjet, a continuous stream of droplets is charged and deflected in an image-wise manner onto the surface of the image-recording element, while un-imaged droplets are caught and returned to an ink sump. Inkjet printers have found broad applications across markets ranging from desktop document and photographic-quality imaging, to short run printing and industrial labeling.
Early inkjet inks were formulated much like conventional printing or pen-applied inks. As greater attention has been directed towards printing speed, ease of use, reliability, and environmental issues and with increasing interest in forming improved images, inks have been formulated to work well on specific media. For example, inks intended to provide durable and glossy images on photo-glossy image receivers can incorporate film forming polymers and soluble dye colorants while inks intended to provide well adhering fast drying, smooth images on plain papers can include soluble dye colorants, paper penetrants and paper anti-curl agents. The soluble dye inks all suffer from light fade, a problem that is especially significant when archival photo-images are desired and from poor resistance to rewetting. It has been proposed to alleviate the light fade problem by providing dispersed pigment as colorants in place of soluble dyes. However, use of pigments often leads to a reduction in image gloss and poor rub resistance on coated media such as photo-glossy media and image inhomogeneity or mottle on plain papers and related untreated media. Jetting has been improved by the use of polymers intended to act as jetting aids.
However, jetting reliability and ink storage stability remains an issue especially with pigmented inks when a low-density forming or light ink is desired as in the preparation and use of the so-called photo-inks and in proofing inks.